Without limiting the scope of the present invention, its background will be described in relation to reservoir stimulation operations performed from a wellbore that traverses a hydrocarbon bearing subterranean formation, as an example.
It is well known in the well drilling and completion art that hydraulic fracturing of a hydrocarbon bearing subterranean formation is sometimes desirable to increase the permeability of the formation in the production interval or intervals adjacent to the wellbore. According to conventional practice, a fracture fluid is pumped through the wellbore into the formation with sufficient volume and pressure to open the desired fractures in the formation. In addition, during certain portions of the fracturing operation, the fracture fluid may carry suitable propping agents, such as sand, gravel or engineered proppants, which are deposited into the fractures and serve the purpose of holding the fractures open following the fracturing operation and providing highly conductive paths for reservoir fluids to the wellbore. Importantly, the success of the fracturing operation is dependent upon the ability to inject large volumes of hydraulic fracture fluid into desired locations within the formation at a high pressure and high flow rate.
It has been found, however, that it is difficult to achieve the desired stimulation in certain completions using conventional fracturing techniques. For example, in horizontal wellbores that may extend several thousand feet through a formation, it may be desirable to perform the fracturing operation in horizontal stages, wherein each stage may be several hundred feet in wellbore length. In such operations, each stage of the wellbore from the toe to the heel may be sequentially perforated, stimulated then isolated. In certain multistage horizontal completions, the plugging and perforating operations may be performed together using wireline techniques.
Due, for example, to residual proppant in uphole sections of the wellbore, it has been found that a wireline conveyed plug and perforate tool string may become stuck in the wellbore during such operations. In this event, while the wireline may be released at the cablehead and retrieved to the surface, this is not desirable as the plug and perforate tool string is left behind in the wellbore. Accordingly, a need has arisen for an improved tool string that is operable to plug and perforate a downhole interval during a multistage horizontal perforating and fracturing operation. A need has also arisen for such an improved tool string that is operable for at least partial retrieval in the event the tool string becomes stuck in the wellbore.